1465. Age-Dependent Interactions Among Clinical Characteristics, Viral Loads and Disease Severity in Young Children with Respiratory Syncytial Virus Infection (RSV) Infection

Abstract Background Differences in clinical presentation and viral loads according to age in young children with RSV, and their correlation with disease severity are poorly defined. The aim of this study was to define age-dependent the differences in demographic, clinical factors and viral loads between children < 2 years of age with mild RSV infection evaluated as outpatients versus those hospitalized with severe RSV infection. Figure 1. Sign and Symptoms according to disease severity and age in infants with RSV infection. Most relevant signs and symptoms were stratified in outpatients (orange) vs inpatients (blue) by age in (A) < 3 months, (B) between 3 and 6 months, and (C) > 6 to 24 months of age. The Y axis represents the signs and symptoms in the two disease severity groups and the X axis the frequency of that specific symptom (%). Numbers next to bars represent the exact number of patients with that specific sign/symptom. Comparisons by Fisher exact test. Symbol (*) indicate significant 2-sided p values Figure 2. Viral load differences according to age in infants with RSV infection. The Y axis represents RSV loads in log10 copies/mL and the X axis differences in viral loads in outpatients (orange) and inpatients (blue) in the three age groups. Comparisons by Mann Whitney test. Methods Previously healthy children < 2 years old with mild (outpatients) and severe (inpatients) RSV infection were enrolled and nasopharyngeal swabs were obtained for RSV typing and quantitation by real-time PCR. Patients were stratified by age (0-< 3, 3-6, and >6-24 months) and multivariable analyses were performed to identify clinical and viral factors associated with severe disease. Results From 2014-2018 we enrolled 534 children with RSV infection: 130 outpatients and 404 inpatients. Median duration of illness was 4 days for both groups, yet viral loads were higher in outpatients than inpatient in the three age groups (Fig 1). Wheezing was more frequent in outpatients of older age (>3 months) than in inpatients (p< 0.01), while fever was more common in inpatients that outpatients (p< 0.01) and increased with age (Fig 2). Adjusted analyses confirmed that increased work of breathing and fever were consistently associated with hospitalization irrespective of age, while wheezing in infants >3 months, and higher RSV loads in children >6-24 months were independently associated with reduced disease severity. Conclusion Age had a significant impact defining the interactions among viral loads, specific clinical manifestations and disease severity in children with RSV infection. These observations highlight the importance of patient stratification when evaluating interventions against RSV. Disclosures Octavio Ramilo, MD, Bill & Melinda Gates Foundation (Grant/Research Support)Janssen (Grant/Research Support, Advisor or Review Panel member)Medimmune (Grant/Research Support)Merck (Advisor or Review Panel member)NIH/NIAID (Grant/Research Support)Pfizer (Consultant, Advisor or Review Panel member)Sanofi/Medimmune (Consultant, Advisor or Review Panel member) Asuncion Mejias, MD, PhD, MsCS, Janssen (Grant/Research Support, Advisor or Review Panel member)Merck (Advisor or Review Panel member)Roche (Advisor or Review Panel member)